Attempts to locate the included module object. Returns the name if not
known.

The scoping rules of Ruby to resolve the name of an included module are:

first look into the children of the current context;

if not found, look into the children of included modules, in reverse
inclusion order;

if still not found, go up the hierarchy of names.

This method has O(n!) behavior when the module calling include
is referencing nonexistent modules. Avoid calling module until after all the files
are parsed. This behavior is due to ruby's constant lookup behavior.

As of the beginning of October, 2011, no gem includes nonexistent modules.